The bump happens with engine/exhaust braking. I would not consider it a deal breaker. If you are expecting it, its really no big deal. In a diesel, I can't imagine it being a huge bump.
If you are really concerned about it, a light touch on the brake controller or even just a light tap on the brakes and all is good.
I travel a lot of mountain roads, and engine braking causes a bump or two semi regularly. I know it and expect it and it's not big deal.
The advantages of the HA or PP FAR OUTWEIGH any bump issues. Get it, you will love it.